Area light source apparatus and liquid crystal display apparatus assembly

ABSTRACT

Disclosed herein is an area light source apparatus for illuminating a liquid crystal display apparatus of the transmission type, which has a display area formed from a plurality of pixels arrayed in a two-dimensional matrix, from the back, including: a plurality of light emitting element assemblies each provided as a light source and each including a light emitting element and a lens through which light emitted from the light emitting element passes; and a plurality of dummy lenses disposed in the proximity of each of the light emitting element assemblies and configured same as the lenses of the light emitting element assemblies.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2006-303788 filed with the Japan Patent Office on Nov. 9,2006, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an area light source apparatus calledbacklight which illuminates a liquid crystal display apparatus of thetransmission type, which has a display area formed from pixels disposedin a two-dimensional matrix, from the back and a liquid crystal displayapparatus assembly which incorporates the area light source apparatus.

2. Description of the Related Art

The liquid crystal material itself in a liquid crystal display apparatusdoes not emit light. Accordingly, for example, a direct area lightsource apparatus (backlight) for illuminating the display area of theliquid crystal display apparatus is disposed rearwardly of the displayarea which is formed from a plurality of pixels. It is to be noted that,in a color liquid crystal display apparatus, one pixel is composed ofthree sub pixels including a red light emitting sub pixel, a green lightemitting sub pixel and a blue light emitting sub pixel. A liquid crystalcell which composes each pixel or each sub pixel is controlled so as tooperate as a kind of an optical shutter (light valve) to control thelight transmittance (numerical aperture) of the pixel or the sub pixelthereby to control the light transmittance for the illumination light(for example, white light) emitted from the area light source apparatusto display an image.

In the past, an area light source apparatus in a liquid crystal displayapparatus assembly illuminates the entire display area with a uniformand fixed brightness. However, an area light source apparatus having aconfiguration different from that of such an area light source apparatusas described above, that is, an area light source apparatus including aplurality of area light source units and having a configuration forvarying the distribution of the luminous intensity over the display areaunits, is in the past known as an area light source apparatus of thepartial driving type or the divisional driving type and disclosed, forexample, in Japanese Patent Laid-Open No. 2005-258403. Control of suchan area light source apparatus as just described is called partialdriving or divisional driving of an area light source apparatus. By suchpartial driving or divisional driving, increase of the contrast ratio byincrease of the white level in the liquid crystal display apparatus anddrop of the black level can be achieved. As a result, enhancement of thequality of image display can be achieved and reduction of the powerconsumption of the area light source apparatus can be anticipated.

A light emitting diode (LED) assembly is frequently used as a lightsource which composes an area light source apparatus. The light emittingdiode assembly includes a plurality of light emitting diodes, and aplurality of lenses through which light emitted from the light emittingdiodes passes. The light passing through each lens has a radiation anglecharacteristic (for example, a Lambertian distribution) based on thecharacteristic of the lenses. Then, the red light emitting diodes, greenlight emitting diodes and blue light emitting diodes are energized toemit red light, green light and blue light, respectively. The red light,green light and blue light are mixed to produce white light, with whichthe display area of the liquid crystal display apparatus is illuminated.It is to be noted that the area light source apparatus includes aplurality of light emitting diode assembly groups each including redlight emitting diode assembles, green light emitting diode assembliesand blue light emitting diode assemblies. The number of red lightemitting diode assemblies, the number of green light emitting diodeassemblies and the number of blue light emitting diode assemblies in onelight emitting diode assembly group and the array pattern of the lightemitting diode assemblies are normally determined based onspecifications of the area light source apparatus. In order to preventoccurrence of color unevenness or luminance unevenness, the lightemitting diode assemblies are frequently gathered in a narrow region.

SUMMARY OF THE INVENTION

Where red light emitting diodes, green light emitting diodes and bluelight emitting diodes in light emitting diode assembly groups areenergized to emit light and the resulting red light, green light andblue light are mixed to produce white light as described above, thelight emitting diodes are disposed in the following manner. Inparticular, a red light emitting diode assembly (R), a green lightemitting diode assembly (G) and a blue light emitting diode assembly (B)which form a light emitting diode assembly group are disposed in such amanner as seen in a schematic view of FIG. 11A in which they are viewedfrom above. Meanwhile, the green light emitting diode assembly (G) andthe blue light emitting diode assembly (B) are disposed as seen in FIG.11B in which they are viewed from sidewardly. It is to be noted that onelight emitting diode assembly group is composed of one red lightemitting diode assembly (R), one green light emitting diode assembly (G)and one blue light emitting diode assembly (B). Further, the lightemitting diode assemblies (R), (G) and (B) are positioned at thevertices of an imaginary equilateral triangle.

In such light emitting diode assemblies (R), (G) and (B), light emittedfrom a certain one of the light emitting diode assemblies (R), (G) and(B) enters and is refracted by a lens which forms the other ones of thelight emitting diode assemblies (R), (G) and (B) and then emerges fromthe lens. Accordingly, the radiation of light emitted from the lightemitting diode assemblies (R), (G) and (B) becomes asymmetrical withrespect to the axes of the light emitting diode assemblies (R), (G) and(B). As a result, in a space above the light emitting diode assemblygroups, a region within which the mixture state of the red light, greenlight and blue light is non-uniform increases, which gives rise to aproblem that color unevenness or luminance unevenness occurs in thespace. Particularly where one area light source unit is energized toemit light in an area light source apparatus of the partial drivingtype, since the influence from the other area light source unitsdisappears, color unevenness or luminance unevenness is likely to standout.

Accordingly, it is demanded to provide an area light source by whichoccurrence of a problem that radiation of light emitted from a lightemitting element assembly becomes asymmetrical with respect to the axisof the light emitting element assembly and this gives rise to occurrenceof color unevenness or luminance unevenness can be prevented withcertainty and a liquid crystal display apparatus assembly whichincorporates the area light source apparatus.

According to an embodiment of the present invention, there is providedan area light source apparatus for illuminating a liquid crystal displayapparatus of the transmission type, which has a display area formed froma plurality of pixels arrayed in a two-dimensional matrix, from theback, including a plurality of light emitting element assemblies eachprovided as a light source and each including a light emitting elementand a lens through which light emitted from the light emitting elementpasses, and a plurality of dummy lenses disposed in the proximity ofeach of the light emitting element assemblies and configured same as thelenses of the light emitting element assemblies.

According to another embodiment of the present invention, there isprovided a liquid crystal display apparatus assembly including a liquidcrystal display apparatus of the transmission type having a display areaformed from a plurality of pixels disposed in a two-dimensional matrix,and an area light source apparatus for illuminating the liquid crystaldisplay apparatus from the back, the area light source apparatusincluding a plurality of light emitting element assemblies each providedas a light source and each including a light emitting element and a lensthrough which light emitted from the light emitting element passes, thearea light source apparatus including a plurality of dummy lenses whichare disposed in the proximity of the light source element assemblies andare same as the lenses included in the light emitting elementassemblies.

In the area light source apparatus and the liquid crystal displayapparatus assembly, while each of the dummy lenses may be formed from alens as a separate item, it may otherwise be formed from an inoperativelight emitting element assembly which has a configuration and structuresame as those of the light emitting element assemblies but is notoperated to emit light. Such an inoperative light emitting elementassembly is hereinafter referred to as dummy light emitting elementassembly. It is to be noted that, where the dummy lens is formed from alens as a separate item, preferably the dummy lens and the lens whichcomposes the light emitting element assembly are same lenses which aresame as each other in terms of the material, shape and so forth. On theother hand, where the dummy lens is formed from a dummy light emittingelement assembly, preferably the light emitting element assembly and thedummy light emitting element assembly are same as each other.

In the area light source apparatus and the liquid crystal displayapparatus assembly which may additionally have the preferredconfiguration described above, preferably each of the dummy lenses isdisposed in a region in which light emitted from the lenses whichcompose the light emitting element assemblies is introduced directlyinto the dummy lens.

Further, in the area light source apparatus and the liquid crystaldisplay apparatus assembly which may additionally have any of thepreferred configurations described above, preferably, in the proximityof any of the light emitting element assemblies, other ones of the lightemitting element assemblies are disposed. In this instance, preferablyone of the light emitting element assemblies is disposed in a region inwhich light emitted from the lens of another one of the light emittingelement assemblies is introduced directly into the light emittingelement assembly. Further, in this instance, preferably a light emittingelement assembly group is composed of a plurality of ones of the lightemitting element assemblies which are positioned at the vertices of oneor a plurality of imaginary regular triangles, and a plurality of onesof the dummy lenses are disposed on the outer side of the light emittingelement assembly group in such a manner as to be positioned at thevertices of imaginary regular triangles of the same shape as that of theimaginary regular triangle. Or, a light emitting element assembly groupmay be composed of a plurality of ones of the light emitting elementassemblies which are positioned at the vertices of one or a plurality ofimaginary squares, and a plurality of ones of the dummy lenses may bedisposed on the outer side of the light emitting element assembly groupin such a manner as to be positioned at the vertices of imaginarysquares of the same shape as that of the imaginary square.

For example, the area light source apparatus and the liquid crystaldisplay apparatus assembly may have such a form that each light emittingelement assembly group is composed of three light emitting elementassemblies which are positioned at the vertices of one imaginary regulartriangle, and nine dummy lenses are disposed in such a manner as to bepositioned at the vertices of an imaginary regular triangle of the sameshape as that of the imaginary regular triangle. Or, the area lightsource apparatus and the liquid crystal display apparatus assembly mayhave such a form that a light emitting element assembly group iscomposed of four light emitting element assemblies which are positionedat the vertices of one imaginary square, and twelve dummy lenses aredisposed in such a manner as to be positioned at the vertices of animaginary square of the same shape as that of the imaginary square. Orelse, the area light source apparatus and the liquid crystal displayapparatus assembly may have such a form that a light emitting elementassembly group is composed of five light emitting element assemblieswhich are positioned at the vertices of two imaginary regular triangles,and fourteen dummy lenses are disposed in such a manner as to bepositioned at the vertices of imaginary regular triangles of the sameshape as that of the imaginary regular triangles.

Or otherwise, dummy lenses may be disposed in rotational symmetry, inpoint symmetry or in line symmetry with respect to an axis of the lightemitting element assembly. In particular, the rotational symmetry maybe, for example, four-fold rotational symmetry, six-fold rotationalsymmetry or eight-fold rotational symmetry with respect to the axis ofthe light emitting element assembly. It is to be noted that, where thedummy lenses are disposed in rotational symmetry, in point symmetry orin line symmetry, if they overlap with some light emitting elementassemblies, then light emitting element assemblies should be disposed inthe regions.

In the area light source apparatus and the liquid crystal displayapparatus assembly which may additionally have the preferredconfiguration described above, a plurality of ones of the light sourcesmay be driven simultaneously in the same driving condition. Or, aplurality of ones of the light sources may be driven partially. Inparticular, the area light source apparatus may be configured such that,where it is assumed that the display area of the liquid crystal displayapparatus is divided into P×Q imaginary display area units, the arealight source apparatus includes P×Q area light source unitscorresponding to the P×Q display area units, the light emitting state ofthe P×Q area light source units being controlled individually, each ofthe area light source units including a light source formed from aplurality of ones of the light emitting element assemblies.

A partition wall may be disposed between adjacent ones of the area lightsource units. The partition walls may be formed from a material which isopaque with respect to light emitted from the light sources provided inthe area light source units such as an acrylic resin, a polycarbonateresin or an ABS resin. Or the partition walls may be formed from amaterial transparent with respect to light emitted from the lightsources provided in the area light source units such as poly methylmethacrylate (PMMA), a polycarbonate resin (PC), a polyallylate resin(PAR), a polyethylene terephthalate resin (PET) or glass. The surface ofthe partition walls may have a light diffusion reflection function ormay have a mirror reflection function. In order to provide the surfaceof the partition walls with a light diffusion reflection function, sandblasting may be applied to form concaves and convexes on the surface ofthe partition walls or a film having concaves and convexes thereon maybe adhered to the surface of the partition walls. On the other hand, inorder to provide the surface of the partition walls with a mirrorreflection function, a light reflecting film may be adhered to thesurface of the partition walls or a light reflecting layer may be formedon the surface of the partition walls, for example, by plating.

In the area light source apparatus and the liquid crystal displayapparatus assembly which may additionally have the preferredconfiguration described above (such apparatus and assembly may behereinafter referred to collectively as present invention), designing ordetermination of specifications of the lenses and the dummy lenses maybe performed finally based on an emerging solid angle or a luminanceprofile of light emitted from each light emitting element assembly, thesize of the liquid crystal display apparatus (or display area unit) tobe illuminated with light emitted from the light emitting elementassembly, a luminance profile necessary for the liquid crystal displayapparatus (or display area unit) and so forth. For example, it ispossible to obtain a light emitting element assembly which includes alens or a dummy lens whose light intensity has an isotropic distributionlike the Lambertian distribution. Also it is possible to obtain a lightemitting element assembly which includes a lens or a dummy lens having atwo-dimensional directional emission configuration by which light isemitted principally in horizontal directions. The lens and the dummylens may be formed from optical glass or a plastic material. Here, theplastic material used to form a plastic lens may be a thermoplasticresin such as an acrylic resin, a polycarbonate resin, a PMMA resin, apolyolefin resin, a polyester resin, a polyurethane resin, polysulfoneresin, polystyrene resin, a vinyl resin or a halogen type resin or athermosetting resin such as an epoxy resin, a polyimide resin, a urearesin, a phenol resin or a silicone resin. A plastic resin can bemolded, for example, by injection molding although it depends upon thematerial. The lens may be fixed by a suitable method in such a manner asto cover the light emitting element, or the lens and the light emittingelement may be formed integrally with each other. In the latter case,the lens may be formed semi-spherically (or in a dome shape) using, forexample, a potting resin, or may be formed using lithography and etchingin combination.

In the present invention, a light emitting diode (LED) may be used forthe light emitting element. Where a light emitting diode is used as thelight source, a red light emitting diode which emits light of a redcolor typically of the wavelength of 640 nm, a green light emittingdiode which emits light of a green color typically of the wavelength of530 nm and blue light emitting diode which emits light of a blue colortypically of the wavelength of 450 nm may be used as a group to obtainwhite light. As occasion demands, an additional light emitting diode ordiodes which emit light of a fourth color, a fifth color and so forthother than the red, green and blue colors may be provided. A lightsource composed of light emitting diodes is preferable in that theoccupation area thereof is small.

More particularly, as a combination of light emitting element assemblieswhich compose a light source, a combination of (one red light emittingelement assembly, one green light emitting element assembly and one bluelight emitting element assembly), another combination of (one red lightemitting element assembly, two green light emitting element assembliesand one blue light emitting element assembly), a further combination of(two red light emitting element assemblies, two green light emittingelement assemblies and one blue light emitting element assembly) or thelike may be used.

A light emitting diode used to form a light source may have a face-upstructure or a flip chip structure. In particular, a light emittingdiode is formed from a substrate and a light emitting layer formed onthe substrate and may have a structure wherein light is emitted to theoutside from the light emitting layer or another structure wherein lightfrom the light emitting layer is emitted to the outside through thesubstrate. More particularly, a light emitting diode (LED) has a layeredstructure, for example, of a first compound semiconductor layer formedon the substrate and having a first conduction type such as, forexample, the n type, an active layer formed on the first compoundsemiconductor layer, and a second compound semiconductor layer formed onthe active layer and having a second conduction type such as, forexample, the p type. The light emitting diode further includes a firstelectrode electrically connected to the first compound semiconductorlayer and a second electrode electrically connected to the secondcompound semiconductor layer. The layers of the light emitting diode maybe formed from known compound semiconductor materials depending upon thewavelength of light to be emitted.

The light emitting diode may be structured such that it further includesa bullet-shaped or dome-shaped cap provided at a portion through whichlight from the light emitting layer is emitted to the outside.Incidentally, if an air layer exists between the light emitting layerand the cap, then a phenomenon that light emitted from the lightemitting layer does not enter the cap immediately but is totallyreflected by the inner face of the cap sometimes occurs. If such aphenomenon as just described occurs, then such a problem occurs that,since the totally reflected light is absorbed back into the lightemitting layer, the light extraction efficiency drops. Accordingly,preferably a filler is filled in the gap between the light emittinglayer and the cap. The filler may be formed from a gel-like material, afluorene acrylic resin, silicone rubber or a silicone oil compound andpreferably has a refractive index of 1.40 or more. More particularly, asthe gel-like material, for example, OCK-451 (refractive index: 1.51) orOCK-433 (refractive index: 1.46) by Nye can be used, or an oil compoundmaterial such as silicone rubber or a silicone oil compound such as, forexample, TSK5353 (refractive index: 1.45) by Toshiba Silicone can beused. It is to be noted that, if the bullet-shaped or dome-shaped capand the filler function as a lens and there is no necessity to provide alens separately, then the cap can be regarded as a lens.

The area light source apparatus includes a light diffusion plate and mayfurther include an optical function sheet group such as a diffusionsheet, a prism sheet and a polarization conversion plate and/or areflecting sheet. The optical function sheet group may be formed fromvarious sheets disposed in a spaced relationship from each other or maybe formed as a layered integral sheet of various layers. The lightdiffusion plate and the optical function sheet group are disposedbetween the area light source apparatus and the liquid crystal displayapparatus.

The liquid crystal display apparatus of the transmission type includes,for example, a front panel having a transparent first electrode, a rearpanel having a transparent second electrode, and a liquid crystalmaterial disposed between the front panel and the rear panel. It is tobe noted that the liquid crystal display apparatus may be amonochromatic liquid crystal display apparatus or a color liquid crystaldisplay apparatus.

The front panel includes a first substrate formed, for example, from aglass substrate or a silicon substrate, a transparent first electrode(also called common electrode and made of, for example, ITO) provided onthe inner face of the first substrate, and a polarizing film provided onthe outer face of the first substrate. Further, where the color liquidcrystal display apparatus is of the transmission type, color filterscoated with an overcoat layer made of an acrylic resin or an epoxy resinare provided on the inner face of the first substrate. For thearrangement pattern of the color filters, a delta array, a stripe array,a diagonal array or a rectangular array may be used. The front panel isfurther configured such that the transparent first electrode is formedon the overcoat layer. It is to be noted that an orientation film isformed on the transparent first electrode. Meanwhile, the rear panelincludes a second substrate formed, for example, from a glass substrateor a silicon substrate, switching elements formed on the inner face ofthe second substrate, transparent second electrodes also called pixelelectrodes and made of, for example, ITO for being controlled by theswitching elements between conducting and non-conducting states, and apolarizing film provided on the outer face of the second substrate. Anorientation film is formed over the overall area including thetransparent second electrodes. The members and the liquid crystalmaterial of the liquid crystal display apparatus including the colorliquid crystal display apparatus of the transmission type may be formedfrom known members and materials. The switching elements may bethree-terminal elements such as MOS FETs or thin film transistors (TFTs)formed on a single crystal silicon semiconductor substrate ortwo-terminal elements such as MIM elements, varistor elements or diodes.

A region in which the transparent first electrode and a secondtransparent electrode overlap with each other and which includes aliquid crystal cell corresponds to one pixel or one sub pixel. In acolor liquid crystal display apparatus of the transmission type, a redlight emitting sub pixel (sometimes referred to as sub pixel [R]) whichcompose each pixel is formed from a combination of a liquid crystal cellwhich forms such a region as described above and a color filter whichtransmits red light therethrough. A green light emitting sub pixel(sometimes referred to as sub pixel [G]) is formed from a combination ofa liquid crystal cell which forms the region and a color filter whichtransmits green light therethrough. A blue light emitting sub pixel(sometimes referred to as sub pixel [B]) is formed from a combination ofa liquid crystal cell which forms the region and a color filter whichtransmits blue light therethrough. The arrangement pattern of the subpixel [R], sub pixel [G] and sub pixel [B] coincides with thearrangement pattern of the color filters described hereinabove. It is tobe noted that one pixel is not limited to that which is composed of aset of three different pixels [R, G, B] including the sub pixel [R], subpixel [G] and sub pixel [B], but may include, for example, in additionto the three different sub pixels [R, G, B], one or a plurality ofdifferent sub pixels. For example, one pixel may include, in addition tothe three different sub pixels [R, G, B], a sub pixel which emits whitelight in order to raise the luminance, sub pixels which emit light ofcomplementary colors in order to expand the color reproduction range, orsub pixels which emit light of yellow and cyan in order to expand thecolor reproduction range.

Here, the light transmittance (also called numerical aperture) Lt of apixel or a sub pixel, the luminance (surface luminance) y of a portionof the display region corresponding to the pixel or sub pixel and theluminance (light source luminance) Y of an area light source unit aredefined in the following manner.

Y₁: for example, highest luminance of the light source luminance. Thisluminance is hereinafter referred to sometimes as light source luminancefirst prescribed value.

Lt₁: for example, maximum value of the light transmittance (numericalaperture) of a pixel or a sub pixel of a display area unit. The valuedescribed is hereinafter referred to some times as light transmittancefirst prescribed value.

Lt₂: light transmittance (numerical aperture) of a pixel or a sub pixelwhen it is assumed that a control signal corresponding to an inputsignal, which is inputted to a driving circuit for driving all pixels,which compose the display area unit, having a value equal to a displayarea unit input signal maximum value x_(u-max) which is a maximum valueamong values of the input signal, is supplied to the pixel or sub pixel.The light transmittance described is hereinafter referred to sometimesas light transmittance second prescribed value. It is to be noted thatthe light transmittances Lt₁ and Lt₂ satisfy a relationship of0≦Lt₁≦Lt₂.

y₂: display luminance obtained when it is assumed that the light sourceluminance is the light source luminance first prescribed value Y₁ andthe light transmittance (numerical aperture) of a pixel or a sub pixelis the light transmittance second prescribed value Lt₂. The displayluminance described is hereinafter referred to sometimes as displayluminance second prescribed value.

Y₂: light source luminance of an area light source unit for setting theluminance of a pixel or a sub pixel to the display second prescribedvalue y₂ when it is assumed that a control signal corresponding to aninput signal having a value equal to the display area unit input signalmaximum value x_(u-max) is supplied to the pixel or sub pixel andbesides it is assumed that the light transmittance (numerical aperture)of the pixel or sub pixel at this time is corrected to the lighttransmittance first prescribe value Lt₁. It is to be noted that thelight source luminance Y₂ is sometimes subjected to correction in whichthe influence of the light source luminance of each area light sourceunit on the light source luminance of any other area light source unitis taken into consideration.

Upon partial driving of the area light source apparatus, the luminanceof a light source which composes an area light source unit correspondingto each display area unit is controlled by a driving circuit so that theluminance of a pixel when it is assumed that a control signalcorresponding to an input signal having a value equal to the displayarea unit input signal maximum value x_(u-max) may be supplied to thepixel, that is, the display luminance second prescribed value y₂ at thelight transmittance first prescribed value Lt₁ may be obtained.Particularly, the light source luminance Y₂ may be controlled, forexample, decreased, so that, for example, the display luminance Y₂ maybe obtained when the light transmittance (numerical aperture) of a pixelor a sub pixel is set, for example, to the light transmittance firstprescribed value Lt₁. In other words, the light source luminance Y₂ ofan area light source unit may be controlled for each image display frameso that, for example, the following expression (1) may be satisfied:

Y ₂ ·Lt ₁ =Y ₁ ·Lt ₂  (1)

Where the number M₀×N₀ of the pixels arranged in a two-dimensionalmatrix is represented by (M₀, N₀), several image display resolutions areavailable including VGA (640, 480), S-VGA (800, 600), XGA (1,024, 768),APRC (1,152, 900, S-XGA (1,280, 1,024), U-XGA (1,600, 1,200), HD-TV(1,920, 1,080), and Q-XGA (2,048, 1,536) as well as (1,920, 1,035),(720, 480) and (1,280, 960). However, the number of pixels is notlimited to any of them. Further, the value of (M₀, N₁₀) and the value of(P, Q) may have any of relationships illustrated in Table 1 belowalthough the relationship between them is not limited to any of them. Asthe number of pixels which compose one display area unit, 20×20 to320×240, preferably 50×50 to 200×200, may be adopted. The number ofpixels may be fixed or may be different among different display areaunits.

TABLE 1 Value of P Value of Q VGA (640, 480) 2~32 2~24 S-VGA (800, 600)3~40 2~30 XGA (1024, 768) 4~50 3~39 APRC (1152, 900) 4~58 3~45 S-XGA(1280, 1024) 4~64 4~51 U-XGA (1600, 1200) 6~80 4~60 HD-TV (1920, 1080)6~86 4~54 Q-XGA (2048, 1536)  7~102 5~77 (1920, 1035) 7~64 4~52 (720,480) 3~34 2~24 (1280, 960) 4~64 3~48

The driving circuit for driving the liquid crystal display apparatus andthe area light source apparatus includes, for example, a light emittingdiode (LED) driving circuit, an area light source apparatus drivingcircuit and an area light source unit driving circuit each of which isformed from an arithmetic operation circuit, a storage device (memory)and so forth, and a liquid crystal display apparatus driving circuitformed from a known circuit such as a timing controller. Control of theluminance (display luminance) of a portion of the display area and theluminance (light source luminance) of the area light source unit isperformed for each one image display frame. It is to be noted that thenumber of images of image information sent for one second as an electricsignal to the driving circuit is a frame frequency (frame rate), and thereciprocal number to the frame frequency is frame time (unit: second).

Thus, in the present invention, in the proximity of each light emittingassembly, dummy lenses same as a lens which forms the light emittingelement assembly are disposed. Accordingly, such a situation that, whenlight emitted from a certain light emitting element assembly enters alens which composes another light emitting element assembly and thenemerges from the lens, radiation of the light emitted from the certainlight emitting element assembly becomes asymmetrical with respect to anaxis of the light emitting element assembly can be prevented. As aresult, occurrence of such a problem that, in a space positioned abovethe light emitting diode assembly group, a region within which themixture state of red light, green light and blue light is non-uniformincreases can be suppressed with certainty.

Further, where the partial driving method (divisional driving method) isadopted in the present invention, since the luminance distribution whenone of the display area units is energized to emit light is uniformized,design for improvement in performance (increase in contrast, reductionin power consumption and so forth) is facilitated. Furthermore, also theluminance distribution when a plurality of display area units areenergized to emit light at the same time is uniformized.

Further, in the present invention, if the partial driving method(divisional driving method) is adopted and the luminance of a lightsource which composes an area light source unit corresponding to eachdisplay area unit is controlled by the driving circuit so that theluminance of a pixel when it is assumed that a control signalcorresponding to an input signal having a value equal to the displayarea unit input signal maximum value x_(u-max) is supplied to the pixelmay be obtained, that is, the display second prescribed value y₂ at thelight transmittance first prescribe value Lt₁ may be obtained, thenreduction of the power consumption of the area light source apparatuscan be achieved. Besides, increase of the white level and reduction ofthe black level can be achieved. Consequently, a high contrast ratiowhich is a ratio in luminance between a full black display portion and afull white display portion which do not include external lightreflection and so forth on the screen surface of the liquid crystaldisplay apparatus can be achieved, and the brightness of a desireddisplay area can be emphasized. Therefore, improvement in the quality ofimage display can be anticipated.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings inwhich like parts or elements denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B is a schematic top plan view showing an area lightsource unit used to form an area light source apparatus according to afirst embodiment of the present invention and a schematic sideelevational view of the area light source unit as viewed in a directionindicated by arrow marks in FIG. 1A, respectively;

FIGS. 2A, 2B and 2C are schematic top plan views showing different arealight source units which form an area light source according to a secondembodiment of the present invention;

FIG. 3 is a schematic sectional view of a light emitting diode;

FIG. 4 is a block diagram illustrating a concept of a liquid crystaldisplay apparatus assembly composed of a color liquid crystal displayapparatus and an area light source apparatus suitable for use with theembodiments of the present invention;

FIG. 5 is a block diagram illustrating a concept of part of a drivingcircuit suitable for use with the embodiments of the present invention;

FIG. 6A is a schematic view showing an arrangement state of lightemitting element assemblies and so forth in the area light sourceapparatus of the embodiments of the present invention and FIG. 6B is aschematic partial sectional view of a liquid crystal display apparatusassembly which includes the color liquid crystal display apparatus andthe area light source apparatus of the embodiments;

FIG. 7 is a schematic partial sectional view of a color liquid crystaldisplay apparatus;

FIG. 8 is a flow chart illustrating a driving method for the liquidcrystal display apparatus assembly according to the first and secondembodiments;

FIG. 9A is a diagram illustrating a relationship between a valueobtained by raising an input signal inputted to an liquid crystaldisplay apparatus driving circuit for driving a sub pixel to the 2.2thpower and the duty ratio and FIG. 9B is a diagram illustrating arelationship between the value of a control signal for controlling thelight transmittance of a sub pixel and the display luminance of the subpixel;

FIGS. 10A and 10B are schematic views illustrating a concept of a stateof adjusting, under the control of an area light source unit drivingcircuit, the light source luminance of an area light source unit so thata display luminance second prescribed value when it is assumed that acontrol signal corresponding to an input signal having a value equal toa display area unit input signal maximum value is supplied to pixels maybe obtained by the area light source unit; and

FIGS. 11A and 11B are a schematic top plan view and a schematic sideelevational view, respectively, of a red light emitting diode assembly,a green light emitting diode assembly and a blue light emitting diodeassembly which compose a light emitting diode assembly group in therelated art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before preferred embodiments of the present invention are described, anoutline of a liquid crystal display apparatus of the transmission typesuitable for use with the embodiments, particularly, a color liquidcrystal display apparatus of the transmission type, and an area lightsource apparatus is described with reference to FIGS. 4, 5, 6A, 6B and7.

It is to be noted that the area light source apparatus described aboveincludes P×Q area light source units corresponding to P×Q imaginarydisplay area units into which the display area of a liquid crystaldisplay apparatus is assumed to be divided. The light emitting state ofthe P×Q area light source units is controlled individually, and a lightsource provided for each area light source unit is formed from aplurality of light emitting element assemblies. Therefore, the arealight source apparatus is formed as an area light source apparatus ofthe partial driving type or divisional driving type. However, the arealight source apparatus is not limited to that of the type justdescribed, but may be of another type wherein a plurality of lightsources are driven simultaneously in a same driving condition.

Referring to FIG. 4, the color liquid crystal display apparatus 10 ofthe transmission type includes a display area 11 in which totaling M₀×N₀pixels are arranged in a two-dimensional matrix such that M₀ pixels arearranged along a first direction and N₀ pixels are arranged in a seconddirection. It is assumed here that the display area 11 is divided intoP×Q imaginary display area units 12. Each of the display area units 12includes a plurality of pixels. In particular, for example, if the imagedisplay resolution of the display area unit 12 satisfies the HD-TVstandards and the number M₀×N₀ of the pixels arranged in atwo-dimensional matrix is represented by (M₀, N₀), then the number is(1,920, 1,080). Further, the display area 11 (indicated by alternatelong and short dash lines in FIG. 4) formed from the pixels arrayed in atwo-dimensional matrix is divided into P×Q imaginary display area units12 (whose boundaries are indicated by alternate long and short dashlines). The value of (P, Q) typically is (19, 12). It is to be noted,however, that the number of display area units 12 (and area light sourceunits 42 hereinafter described) in FIG. 4 is different from the typicalnumber for the simplified illustration of the drawing. Each of thedisplay area units 12 is composed of a plurality of (M×N) pixels, andthe number of pixels which form one display area unit 12 is, forexample, approximately 10,000. Each of the pixels is composed of a setof a plurality of sub pixels which emit light of different colors. Moreparticularly, each pixel is composed of three different sub pixelsincluding a red light emitting sub pixel (sub pixel [R]), a green lightemitting sub pixel (sub pixel [G]) and a blue light emitting sub pixel(sub pixel [B]). The color liquid crystal display apparatus 10 of thetransmission type is line sequentially driven. More particularly, thecolor liquid crystal display apparatus 10 includes scanning electrodes(extending along the first direction) and data electrodes (extendingalong the second direction) which cross each other in a matrix. Thecolor liquid crystal display apparatus 10 inputs a scanning signal tothe scanning electrodes to select the scanning electrodes to display animage, that is, one screen image, based on a data signal (based on acontrol signal) inputted to the data electrodes.

Referring to FIG. 7, the color liquid crystal display apparatus 10includes a front panel 20 having a transparent first electrode 24, arear panel 30 having transparent second electrodes 34, and a liquidcrystal material 13 disposed between the front panel 20 and the rearpanel 30.

The front panel 20 includes a first substrate 21 formed, for example,from a glass substrate, and a polarizing film 26 provided on the outerface of the first substrate 21. Color filters 22 are provided on theinner face of the first substrate 21 and are coated with an overcoatlayer 23 made of an acrylic resin or an epoxy resin. The transparentfirst electrode 24 (called common electrode and made of, for example,ITO) is formed on the overcoat layer 23, and an orientation film 25 isformed on the transparent first electrode 24. Meanwhile, the rear panel30 includes a second substrate 31 formed, for example, from a glasssubstrate, and switching elements 32 (particularly in the form of a thinfilm transistor TFT) formed on the inner face of the second substrate31. The rear panel 30 further includes the transparent second electrodes34 (also called pixel electrodes and made of, for example, ITO) forbeing controlled by the switching elements 32 between conducting andnon-conducting states, and a polarizing film 36 provided on the outerface of the second substrate 31. An orientation film 35 is formed overthe overall area including the transparent second electrodes 34. Thefront panel 20 and the rear panel 30 are joined together at outerperipheries thereof using a bonding agent (not shown). It is to be notedthat the switching elements 32 need not be TFTs but may be formed, forexample, from MIM elements. Further, an insulating film 37 is providedbetween adjacent ones of the switching elements 32.

Since the members and the liquid crystal material of the color liquiddisplay apparatus of the transmission type may be selected from knownmembers and materials, detailed description of them is omitted herein.

Referring back to FIG. 4, a direct type area light source apparatus 40(backlight) includes P×Q area light source units 42 corresponding to theP×Q imaginary display area units 12. Each of the area light source units42 illuminates one of the display area units 12 which corresponds to thearea light source unit 42 from the back thereof. The light sourcesprovided in the area light source units 42 are controlled individually.However, the light source luminance of each area light source unit 42 isnot influenced by the light emitting state and so forth of the lightsources provided in the other area light source units 42. Further, whilethe area light source apparatus 40 is positioned below the color liquidcrystal display apparatus 10, the color liquid crystal display apparatus10 and the area light source apparatus 40 are shown separately from eachother in FIG. 4. The arrangement state of the light emitting elementassemblies and so forth of the area light source apparatus 40 isschematically illustrated in FIG. 6A, and a schematic partial section ofthe liquid crystal display apparatus assembly formed from the colorliquid crystal display apparatus 10 and the area light source apparatus40 is shown in FIG. 6B. Referring to FIGS. 6A and 6B, each light sourceis formed from a light emitting element assembly 100 which is driven inaccordance with a pulse width modulation (PWM) control method.Adjustment of the luminance of each area light source unit 42 isperformed through increasing or decreasing control of the duty ratio inpulse width modulation control of the light emitting element assembly100 which forms the area light source unit 42.

As seen from the schematic partial section of the liquid crystal displayapparatus assembly in FIG. 6B, the area light source apparatus 40includes a housing 51 which in turn includes an outer side frame 53 andan inner side frame 54. An end portion of the color liquid crystaldisplay apparatus 10 of the transmission type is held between and by theouter side frame 53 and the inner side frame 54 with spacers 55A and 55Binterposed therebetween, respectively. Further, a guide member 56 isdisposed between the outer side frame 53 and the inner side frame 54 sothat the color liquid crystal display apparatus 10 held between theouter side frame 53 and the inner side frame 54 may not be displaced.Details of the area light source units 42 are hereinafter described. Alight diffusion plate 61 is attached to the inner side frame 54 througha spacer 55C and a bracket member 57 at an upper portion of the insideof the housing 51. Further, optical function sheets such as a diffusionsheet 62, a prism sheet 63 and a polarization conversion sheet 64 arelayered on the light diffusion plate 61.

A reflection sheet 65 is provided at a lower portion of the inside ofthe housing 51. The reflection sheet 65 is attached to a bottom face 52Aof the housing 51 through an attaching member not shown such that areflecting face thereof is opposed to the light diffusion plate 61. Thereflection sheet 65 may be formed from an increased silver reflectingfilm having a structure that a silver reflecting film, a low refractiveindex film and a high refractive index film are layered in order on asheet substrate. The reflection sheet 65 reflects light emitted from aplurality of light emitting element assemblies 100 and light reflectedby a side face 52B of the housing 51 or a partition wall 41 shown inFIG. 6A. Thus, red light, green light and blue light emitted from redlight emitting element assemblies 100R which emit red light, green lightemitting element assemblies 100G which emit green light and green lightemitting element assemblies 100B which emit blue light can be mixed toproduce white light of high color purity as illumination light. Theillumination light is emitted from the area light source units 42through the light diffusion plate 61 and passes through the opticalfunction sheets such as the diffusion sheet 62, prism sheet 63 andpolarization conversion sheet 64 to illuminate the color liquid crystaldisplay apparatus 10 from the back.

Photodiodes 43R, 43G, 43B as optical sensors are disposed in theproximity of the bottom face 52A of the housing 51. It is to be notedthat the photodiode 43R has a red filter attached thereto for measuringthe intensity of red light; the photodiode 43G has a green filterattached thereto for measuring the intensity of green light; and thephotodiode 43B has a blue filter attached thereto for measuring theintensity of blue light. Here, one set of optical sensors (photodiodes43R, 43G, 43B) is disposed for each area light source unit 42. Thephotodiodes 43R, 43G, 43B as optical sensors measure the luminance andthe chromaticity of the light emitting diodes 101R, 101G, 101B,respectively.

Referring to FIGS. 4 and 5, driving circuits for driving the area lightsource apparatus 40 and the color liquid crystal display apparatus 10 inresponse to an input signal from the outside (display circuit) includean area light source apparatus control circuit 70 and area light sourceunit driving circuits 80 for performing on/off control of the red lightemitting diodes 101R which form the red light emitting elementassemblies 100R, green light emitting diodes 101G which form the greenlight emitting element assemblies 100G and blue light emitting diodes101B which form the blue light emitting element assembly 100B, of thearea light source apparatus 40 in accordance with a pulse widthmodulation control method. The driving circuit further includes a liquidcrystal display apparatus driving circuit 90.

The area light source apparatus control circuit 70 includes anarithmetic operation circuit 71 and a storage device (memory) 72.Meanwhile, each of the area light source unit driving circuits 80includes an arithmetic operation circuit 81, a storage device (memory)82, an LED driving circuit 83, a photodiode control circuit 84,switching elements 85R, 85G, 85B each formed from an FET, and a lightemitting diode driving circuit 86 in the form of a constant currentsource. The circuits and elements mentioned which compose the area lightsource apparatus control circuit 70 and area light source unit drivingcircuits 80 may be formed from individually known circuits. Meanwhile,the liquid crystal display apparatus driving circuit 90 for driving thecolor liquid crystal display apparatus 10 is formed from a known circuitsuch as a timing controller 91. The color liquid crystal displayapparatus 10 includes gate drivers, source drivers and so forth (all notshown) for driving the switching elements 32 each of which forms aliquid crystal cell and is formed from a TFT.

The light emitting state of the light emitting diodes 101R, 101G, 101Bin a certain image display frame is measured by the photodiodes 43R,43G, 43B, and outputs of the photodiodes 43R, 43G, 43B are inputted tothe photodiode control circuit 84 and converted into data (signals), forexample, of the luminance and the chromaticity of the light emittingdiodes 101R, 101G, 101B by the photodiode control circuit 84 and thearithmetic operation circuit 81. The data are sent to the LED drivingcircuit 83, by which the light emitting state of the light emittingdiodes 101R, 101G, 101B in a next image data display frame is controlledbased on the data. In this manner, a feedback mechanism is formed.

Resistors r_(R), r_(G), r_(B) for current detection are inserted inseries to the light emitting diodes 101R, 101G, 101B on the downstreamof the light emitting diodes 101R, 101G, 101B, respectively, and currentflowing through the resistors r_(R), r_(G), r_(B) is converted intovoltages. Operation of the light emitting diode driving circuit 86 iscontrolled under the control of the LED driving circuit 83 so that thevoltage drops of the resistors r_(R), r_(G), r_(B) may have apredetermined value. While the single light emitting diode drivingcircuit (constant current source) 86 is shown in FIG. 5, actually lightemitting diode driving circuits 86 for individually driving the lightemitting diodes 101R, 101G, 101B are provided.

While the display area 11 including pixels arranged in a two dimensionalmatrix are divided in P×Q display area units, where this state isrepresented in “row” and “column”, it is considered that the displayarea 11 is divided in display area units of P rows×Q columns. Further,while each display area unit 12 is formed from a plurality of (M×N)pixels, where this state is represented in “row” and “column”, it isconsidered that the display area unit 12 is formed from pixels of Nrows×M columns. Further, a red light emitting sub pixel (sub pixel [R]),a green light emitting sub pixel (sub pixel [G]) and a blue lightemitting sub pixel (sub pixel [B]) are sometimes referred tocollectively as “sub pixels [R, G, B]”. Further, a red light emittingsub pixel control signal, a green light emitting sub pixel controlsignal and a blue light emitting sub pixel control signal inputted tothe sub pixels [R, G, B] for control of operation of the sub pixels [R,G, B] (particularly, for example, for control of the light transmittance(numerical aperture)) are sometimes referred to collectively as “controlsignals [R, G, B]”. Furthermore, a red light emitting sub pixel inputsignal, a green light emitting sub pixel input signal and a blue lightemitting sub pixel input signal inputted from the outside to the drivingcircuits for driving the sub pixels [R, G, B] which compose a displayarea unit are sometimes referred to collectively as “input signals [R,G, B]”.

Each pixel is composed of a set of three different sub pixels includinga red light emitting sub pixel (sub pixel [R]), a green light emittingsub pixel (sub pixel [G]) and a blue right emitting sub pixel (sub pixel[B]). In the following description, control (gradation control) of theluminance of each of the sub pixels [R, G, B] is performed in 8 bits andhence at 2⁸ stages from 0 to 255. Accordingly, each of the values x_(R),x_(G), x_(B) of the input signals [R, G, B] inputted to the liquidcrystal display apparatus driving circuit 90 in order to drive the subpixels [R, G, B] of each of the pixels which compose the display areaunits 12 can assume values of 2⁸ stages. Also the values S_(R), S_(G),S_(B) of pulse width modulation output signals for controlling the lightemission time of the red light emitting element assembly 100R, greenlight emitting element assembly 100G and blue light emitting elementassembly 100B which compose each area light source unit can assume thevalues of 2⁸ stages from 0 to 255. It is to be noted that the valuesmentioned above are not particularly limited to those value given above.For example, 10-bit control may be adopted instead so that the controlcan be performed among 2¹⁰ stages from 0 to 1,023. In this instance, arepresentation of a numerical value of 8 bits may be, for example,multiplied by four.

To each pixel, a control signal for controlling the light transmittanceLt of the pixel is supplied from a driving circuit. In particular,control signals [R, G, B] for controlling the light transmittance Lt ofsub pixels [R, G, B] are supplied from the liquid crystal displayapparatus driving circuit 90 to the sub pixels [R, G, B], respectively.In particular, the liquid crystal display apparatus driving circuit 90produces control signals [R, G, B] from input signals [R, G, B] inputtedthereto and supplies or outputs the control signals [R, G, B] to the subpixels [R, G, B]. It is to be noted that, since the light sourceluminance Y₂ which is the luminance of an area light source unit 42 isvaried for each one image display frame, the control signals [R, G, B]have values x_(R-corr), x_(G-corr), x_(B-corr) obtained, for example, byperforming correction (compensation) based on the variation of the lightsource luminance Y₂ for values obtained by raising the values x_(R),x_(G), x_(B) of the input signals [R, G, B] to the 2.2th power. Then,the control signals [R, G, B] are signaled by a known method from thetiming controller 91 of the liquid crystal display apparatus drivingcircuit 90 to the gate drivers and the source drivers of the colorliquid crystal display apparatus 10. Thus, the switching elements 32which form the sub pixels are driven in accordance with the controlsignals [R, G, B] to apply desired voltages to the transparent firstelectrode 24 and the transparent second electrodes 34 which compose theliquid cells thereby to control the light transmittance Lt (numericalaperture) of the sub pixels. Here, as the values x_(R-corr), x_(G-corr),x_(B-corr) of the control signals [R, G, B] increase, the lighttransmittances (numerical apertures) Lt of the sub pixels [R, G, B]increase and the luminance (display luminance y) at a portion of thedisplay region corresponding to the sub pixels [R, G, B] increases. Inother words, the image formed from light which passes through the subpixels [R, G, B] (usually having a form of dot) becomes brighter.

The control of the display luminance y and the light source luminance Y₂is performed for each one image display frame, for each display areaunit and for each area light source unit in image display of the colorliquid crystal display apparatus 10. Further, operation of the colorliquid crystal display apparatus 10 and operation of the area lightsource apparatus 40 in one image display frame are synchronized witheach other. It is to be noted that the number of pieces of imageinformation sent as an electric signal to the driving circuits for onesecond, that is, the number of images per one second, is the framefrequency (frame rate), and the reciprocal number to the frame frequencyis frame time (unit: second).

Embodiment 1

The Embodiment 1 according to the present invention relates to an arealight source apparatus and a liquid crystal display apparatus assembly.FIG. 1 a shows an area light source unit 42 of the area light sourceapparatus 40 according to the Embodiment 1 as viewed from above, andFIG. 1B shows the area light source unit 42 as viewed from sidewardly asviewed in the direction indicated by an arrow mark in FIG. 1A.

The area light source apparatus 40 includes P×Q area light source units42 as described hereinabove. Each of the area light source units 42includes a plurality of light emitting element assemblies 100R, 100G,100B each including a light emitting element (light emitting diode 101)and a lens 102 through which light emitted from the light emittingelement (light emitting element 101) passes and serving as a lightsource. The light emitting element assemblies 100R, 100G, 100B aresecured to the bottom face 52A of the housing 51 by a suitable method.Further, the lens 102 is secured using a bonding agent in such a manneras to cover the light emitting element (light emitting diode 101). It isto be noted that the lens 102 may be secured by caulking to the lightemitting element (light emitting diode 101). The light emitting diodes101R, 101G, 101B are driven in accordance with a pulse width modulation(PWM) control method, and the red light emitting diode 101R emits lightof a red color (for example, of a wavelength 640 nm); the green lightemitting diode 101G emits light of a green color (for example, of awavelength of 530 nm); and the blue light emitting diode 101B emitslight of a blue color (for example, of a wavelength of 450 nm).

Dummy lenses 110 same as the lens 102 used to form the light emittingelement assemblies 100R, 100G, 100B are disposed in the proximity of thelight emitting element assemblies 100R, 100G, 100B. In particular, eachof the dummy lenses 110 is formed from an inoperative light emittingelement assembly (which has a same configuration and structure as thoseof the light emitting element assemblies but does not emit light).However, the dummy lenses 110 need not have the configuration justdescribed, but each of the dummy lenses 110 may be formed from a singlelens. The dummy lenses 110 are disposed particularly in a region inwhich light emitted from the lens 102 which composes each light emittingelement assembly 100 enters directly into the dummy lenses 110. Thelenses 102 and the dummy lenses 110 are produced by injection moldingfrom an acrylic resin material and are designed so as to obtain lightemitting element assemblies which exhibit an isotropic light intensitydistribution like the Lambertian distribution. It is to be noted that,in FIG. 1A and also in FIGS. 2A, 2B and 2C, the light emitting elementassemblies 100R, 100G, 100B are indicated by round marks to which “R”,“G” and “B” are applied, respectively.

When light emitted from a certain light emitting element assembly entersa lens which composes a different light emitting element assembly andthen emerges from the lens in this manner, such a situation thatradiation of the light emitted from the certain light emitting elementassembly becomes asymmetrical with respect to an axis of the lightemitting element assembly can be prevented due to the presence of thedummy lenses 110. As a result, occurrence of such a problem that, in aspace above the light emitting diode assembly group, a region withinwhich the mixture state of red light, green light and blue light isnon-uniform increases can be suppressed with certainty. It is to benoted that, in FIG. 1B, light emitted from a certain light emittingelement assembly (green light emitting element assembly 100G or 100B)and entering and emerging from a dummy lens 110 is indicated by a solidline. Meanwhile, an emerging state of light emitted from a certain lightemitting element assembly (light emitting element assembly 100G or 100B)where no dummy lens 110 exists is indicated by a broken line.

Further, in the Embodiment 1, different light emitting elementassemblies are disposed in the proximity of each one light emittingelement assembly. Such different light emitting element assemblies aredisposed in a region wherein light emitted from a lens of the one lightemitting element assembly directly enters the different light emittingelement assemblies.

In the Embodiment 1, one light emitting element assembly group is formedfrom a plurality of light emitting element assemblies positioned at thevertices of one imaginary regular triangle indicated by broken lines,particularly, from one red light emitting element assembly 100R, onegreen light emitting element assembly 100G and one blue light emittingelement assembly 100B. Further, a plurality of dummy lenses,particularly, nine dummy lenses 110, are disposed so as to bepositioned, on the outer side of the one light emitting element assemblygroup, at the vertices of imaginary regular triangles of the same shapeas that of the imaginary regular triangle.

Each light emitting diode 101 has such a section as seen in FIG. 3.Referring to FIG. 3, the light emitting diode 101 shown includes a lightemitting layer 120 secured to a substrate, and a cap 130 made of aplastic material. In particular, the cap 130 is placed at a lightemerging portion of the light emitting layer 120. The cap 130 covers thelight emitting layer 120 with a space 131 interposed therebetween. Moreparticularly, the light emitting layer 120 is fixed to a sub mount 121and electrically connected to external electrodes 125A and 125B throughwiring lines (not shown) provided on the sub mount 121 and gold wires124A and 124B. The external electrodes 125A and 125B are electricallyconnected to a driving circuit (not shown). The sub mount 121 isattached to a heat sink 122 by a bonding agent, and the heat sink 122 isattached to the support member 123. A filler 140 which is transparentwith respect to light emitted from the light emitting layer 120 isfilled in the space 131 between the cap 130 and the light emitting diode101. The cap 130 is made of an acrylic resin material and molded byinjection molding. Further, the substrate is formed from a supportmember 123 made of a PMMA resin material and molded by injection moldingand the heat sink 122. The filler 140 is made of a gel-like material, afluorene type acrylic resin material, silicone rubber or a silicon oilcompound and has a refractive index of 1.40 or more. More particularly,as the gel-like material, for example, OCK-451 (refractive index: 1.51)or OCK-433 (refractive index: 1.46) by Nye can be used, or an oilcompound material such as silicone rubber or a silicone oil compoundsuch as, for example, TSK5353 (refractive index: 1.45) by ToshibaSilicone can be used. Since such a filler 140 as described is filled inthe space 131, light emitted from the light emitting layer 120 canadvance into the cap 130 with certainty without being totally reflectedby the cap 130. In other words, if light emitting from the lightemitting layer 120 is totally reflected by the cap 130, then since thetotally reflected light is re-absorbed into the light emitting layer120, such a problem that the light extraction efficiency drops occurs.However, where the filler 140 is filled in the space 131, occurrence ofsuch a problem as just described can be prevented with certainty.

Embodiment 2

The Embodiment 2 is a modification to the Embodiment 1. The area lightsource unit 42 of the area light source apparatus 40 according to theEmbodiment 2 may have such top plan arrangements as seen in FIGS. 2A, 2Band 2C. In the arrangement shown in FIG. 2A, one light emitting elementassembly group is formed from a plurality of light emitting elementassemblies, particularly one red light emitting element assembly 100R,two green light emitting element assemblies 100G and one blue lightemitting element assembly 100B, positioned at the vertices of oneimaginary square (indicated by broken lines). Further, a plurality ofdummy lenses, particularly 12 dummy lenses 110, are disposed on theouter side of the light emitting element assembly group such that theyare positioned at the vertices of imaginary squares of a shape same asthat of the imagery square. Meanwhile, in the arrangement shown in FIG.2B, one light emitting element assembly group is formed from a pluralityof light emitting element assemblies, particularly one red lightemitting element assembly 100R, two green light emitting elementassemblies 100G and two blue light emitting element assemblies 100B,positioned at the vertices of two imaginary regular triangles indicatedby broken lines. Further, a plurality of dummy lenses, particularly 14light emitting element assemblies 100, are disposed on the outer side ofthe light emitting element assembly group such that they are positionedat the vertices of imaginary regular triangles having a shape same asthat of the imaginary regular triangle. Further, in the arrangementshown in FIG. 2C, one light emitting element assembly group is formedfrom a plurality of light emitting element assemblies, particularly oneblue light emitting element assembly 100B, two red light emittingelement assemblies 100R and two green light emitting element assemblies10G, disposed in a cross shape. Further, a plurality of dummy lenses,particularly eight light emitting element assemblies 100, are disposedon the outer side of the light emitting element assembly group such thateach of them is positioned at the center of a cross shape. Except thefeatured described above, the area light source apparatus 40 or thecolor liquid crystal display apparatus 10 may have a configuration andstructure similar to those of the area light source apparatus 40 or thecolor liquid crystal display apparatus 10 of the Embodiment 1.Therefore, more detailed description of the configuration or structureis omitted herein to avoid redundancy.

In the following, a driving method for a liquid crystal displayapparatus assembly in the Embodiment 1 and the Embodiment 2 is describedwith reference to FIGS. 4, 5 and 8. It is to be noted that FIG. 8illustrates a driving method for the liquid crystal display apparatusassembly in the Embodiment 1 and the Embodiment 2.

In the Embodiment 1 and the Embodiment 2, a control signal forcontrolling the light transmittance Lt of a pixel is supplied to each ofthe pixels from the driving circuit. More particularly, control signals[R, G, B] for controlling the light transmittance Lt of the sub pixels[R, G, B] which compose each pixel are supplied from the liquid crystaldisplay apparatus driving circuit 90 to the sub pixels [R, G, B]. Then,in each of the area light source units 42, the luminance of the lightsource which compose the area light source unit 42 corresponding to adisplay area unit 12 is controlled by the area light source apparatuscontrol circuit 70 and an area light source unit driving circuit 80 sothat the luminance of all of the pixels which compose the display areaunit 12, that is, a display luminance second prescribed value y₂ at alight transmittance first prescribed value Lt₁, may be obtained where itis assumed that a control signal corresponding to an input signal havinga value equal to a display area unit input signal maximum valuex_(u-max), which is a maximum value among the values x_(R), x_(G), x_(B)of the input signals [R, G, B] inputted to the driving circuits 70, 80and 90 in order to drive all pixels (sub pixels [R, G, B]) of thedisplay area unit 12. More particularly, the light source luminance Y₂may be controlled, for example, decreased, so that, for example, thedisplay luminance second prescribed value y₂ may be obtained when thelight transmittance (numerical aperture) of the pixels or sub pixels isset to the light transmittance first prescribed value Lt₁. In otherwords, the light source luminance Y₂ may be controlled for each imagedisplay frame so that, for example, the following expression (1) may besatisfied:

Y ₂ ·Lt ₁ =Y ₁ ·Lt ₂  (1)

where y₂ and Y₂ have a relationship of Y₂≦Y₁.

[Step-100]

Input signals [R, G, B] and a clock signal CLK for one image displayframe signaled from a known display circuit such as a scan converter areinputted to the area light source apparatus control circuit 70 and theliquid crystal display apparatus driving circuit 90 (refer to FIG. 4).It is to be noted that the input signals [R, G, B] are output signals,for example, from an image pickup tube when the input light amount tothe image pickup tube is y′ and are input signals which are outputted,for example, from a broadcasting station and inputted also to the liquidcrystal display apparatus driving circuit 90 in order to control thelight transmittance Lt of the pixels, and can be represented by afunction of the input light amount y′ to the 0.45th power. The valuesx_(R), x_(G), x_(B) of the input signals [R, G, B] for one image displayframe inputted to the area light source apparatus control circuit 70 arestored once into the storage device (memory) 72 which composes the arealight source apparatus control circuit 70. Meanwhile, also the valuesx_(R), x_(G), x_(B) of the input signals [R, G, B] for one image displayframe inputted to the liquid crystal display apparatus driving circuit90 are stored once into a storage device (not shown) which composes theliquid crystal display apparatus driving circuit 90.

[Step-110]

Then, in the arithmetic operation circuit 71 which composes the arealight source apparatus control circuit 70, the values of the inputsignals [R, G, B] stored in the storage device 72 are read out. Then,the arithmetic operation circuit 71 determines the display area unitinput signal maximum value x_(u-max) which is a maximum value among thevalues x_(R), x_(G), x_(B) of the input signals [R, G, B] for drivingthe sub pixels [R, G, B] in all pixels which compose the (p, q)thdisplay area unit 12 [first, p=1, q=1]. Then, the display area unitinput signal maximum value x_(u-max) is stored into the storage device72. The processes at this step are executed for all of m=1, 2, . . . ,M, n=1, 2, . . . , N, that is, for all of the M×N pixels.

For example, where x_(R) has a value corresponding to “110” and x_(G)has another value corresponding to “150” while x_(B) has a valuecorresponding to “50”, the display area unit input signal maximum valuex_(u-max) has a value corresponding to “150”.

This operation is repeated from (p, q)=(1, 1) to (p, q)=(P, Q), and thedisplay area unit input signal maximum values x_(u-max) of all displayarea units 12 are stored into the storage device 72.

[Step-120]

Then, the light source luminance Y₂ of the area light source unit 42corresponding to the display area unit 12 is adjusted under the controlof the area light source unit driving circuit 80 so that the luminancewhen it is assumed that the control signals [R, G, B] corresponding tothe input signals [R, G, B] having values equal to the display area unitinput signal maximum value x_(u-max) are supplied to the sub pixels [R,G, B], that is, the display luminance second prescribed value y₂ at thelight transmittance first prescribed value Lt₁, may be obtained by thearea light source unit 42. In particular, the light source luminance y₂may be controlled for each one image display frame and for each one arealight source unit so that the expression (1) given hereinabove may besatisfied. More particularly, the luminance of the light emittingelement assembly 100 may be controlled based on an expression (2) givenbelow which represents a light source luminance control functiong(x_(nol-max)) while the light source luminance Y₂ is controlled so asto satisfy the expression (1). A concept of such control as justdescribed is illustrated in FIGS. 10A and 10B. It is to be noted,however, that, as hereinafter described, correction based on theinfluence of other area light source units 42 is performed for the lightsource luminance Y₂ as occasion demands. Further, as hereinafterdescribed, the relationships relating to the control of the light sourceluminance Y₂, that is, the relationship among the display area unitinput signal maximum value x_(u-max), the values of the control signalscorresponding to the input signals having a value equal to the displayarea unit input signal maximum value x_(u-max), the display luminancesecond prescribed value y₂ when it is assumed that such control signalsare supplied to the pixels (sub pixels), the light transmittance(numerical aperture) [light transmittance second prescribed value Lt₂]of the sub pixels at this time and the luminance control parameters inthe area light source units 42 with which the display luminance secondprescribed value y₂ is obtained where the light transmittance (numericalaperture) of the sub pixels is set to the light transmittance firstprescribed value Lt₁ and so forth may be determined in advance andstored into the storage device 72 or the like.

g(x _(nol-max))=a ₁·(x _(nol-max))^(2.2) +a ₀  (2)

Here, where the maximum value of the input signals (input signals [R, G,B]) inputted to the liquid crystal display apparatus driving circuit 90in order to drive the pixels (or the sub pixels [R, G, B] which composethe pixels) is represented by x_(max), it can be represented by

x_(nol-max)≡x_(u-max)/x_(max)

where a₁ and a₀ are constants and satisfy

a ₁ +a ₀=1

0<a₀<1,0<a₁<1

For example, the constants a₁ and a₀ may be set to

a₁=0.99

a₀=0.01

Further, since each of the values x_(R), x_(G), x_(B) of the inputsignals [R, G, B] can assume values of 2⁸ stages, the value of x_(max)corresponds to “255”.

Incidentally, in the area light source apparatus 40, for example, ifluminance control of the (p, q)=(1, 1) area light source unit 42 isassumed, then it is sometimes necessary to take the influence from theother P×Q area light source units 42 into consideration. Since such aninfluence upon the area light source unit 42 from the other area lightsource units 42 is known in advance from a light emission profile ofeach area light source unit 42, the difference can be calculated bybackward calculation, and consequently, correction can be performedbased on the difference. A basic form of the arithmetic operation isdescribed below.

The luminance (light source luminance Y₂) necessary for the P×Q arealight source units 42 based on the requirements of the expressions (1)and (2) is represented by a matrix [L_(P×Q)]. Meanwhile, the luminanceof a certain area light source unit obtained when only the certain arealight source is driven while the other area light source units are notdriven is determined in advance with regard to the P×Q area light sourceunits 42. The luminance mentioned is represented by a matrix [L′_(P×Q)].Further, correction coefficients are represented by a matrix [α_(P×Q)].In this instance, a relationship of the matrices can be represented bythe following expression (3-1). The matrix [α_(P×Q)] of the correctioncoefficients can be determined in advance.

[L _(P×Q) ]=[L′ _(P×Q) ]·[α _(P×Q)]  (3-1)

Therefore, the matrix [L′_(P×Q)] may be determined from the expression(3-1). The matrix [L′_(P×Q)] can be determined by arithmetic operationof an inverse matrix. That is,

[L′ _(P×Q) ]=[L _(P×Q) ]·[α _(P×Q)]  (3-2)

should be calculated. Then, the light sources (light emitting elementassemblies 100) provided in the area light source units 42 should becontrolled so that the luminance values represented by the matrix[L′_(P×Q)] may be obtained. In particular, such operation and processmay be performed using information (data table) stored in the storagedevice (memory) 82. It is to be noted that, since, in the control of thelight emitting element assemblies 100, the values of the matrix[L′_(P×Q)] may not assume negative values, naturally it is necessary tocause a result of the arithmetic operation to remain within the positiveregion. Accordingly, the solution of the expression (3-2) may be not anexact solution but an approximate solution.

The matrix [L′_(P×Q)] of the luminance when it is assumed that an arealight source unit is driven solely as described above is determinedbased on the matrix [L_(P×Q)] and the matrix [α_(P×Q)] of correctioncoefficients obtained based on the values of the expressions (1) and (2)obtained by the arithmetic operation circuit 71 of the area light sourceapparatus control circuit 70 in this manner. Further, the matrix[L′_(P×Q)] of the luminance is converted into integers within the rangeof 0 to 255, that is, values of the pulse width modulation outputsignal. In this manner, the arithmetic operation circuit 71 of the arealight source apparatus control circuit 70 can determine the value S_(R)of the pulse width modulation output signal for controlling the lightemission time of the red light emitting diode 101R in the area lightsource unit 42, the value S_(G) of the pulse width modulation outputsignal for controlling the light emission time of the green lightemitting diode 101G and the value S_(B) of the pulse width modulationoutput signal for controlling the light emission time of the blue lightemitting diode 101B.

[Step-130]

Then, the values S_(R), S_(G), S_(B) of the pulse width modulationoutput signals obtained by the arithmetic operation circuit 71 of thearea light source apparatus control circuit 70 are signaled to thestorage device 82 of the area light source unit driving circuit 80provided corresponding to the area light source unit 42 and stored intothe storage device 82. Also the clock signal CLK is signaled to the arealight source unit driving circuit 80 (refer to FIG. 5).

[Step-140]

Then, the arithmetic operation circuit 81 determines on time t_(R-ON)and off time t_(R-OFF) of the red light emitting diode 101R of the arealight source unit 42, on time t_(R-ON) and off time t_(G-OFF) of thegreen light emitting diode 101G and on time t_(B-ON) and off timet_(B-OFF) of the blue light emitting diode 101B based on the valuesS_(R), S_(G), S_(B) of the pulse width modulation output signal. It isto be noted that

$\begin{matrix}{{t_{R\text{-}{ON}} + t_{R\text{-}{OFF}}} = {t_{G\text{-}{ON}} + t_{G\text{-}{OFF}}}} \\{= {t_{B\text{-}{ON}} + t_{B\text{-}{OFF}}}} \\{= {{fixed}\mspace{14mu} {value}\mspace{14mu} t_{Const}}}\end{matrix}$

Meanwhile, the duty ratio in driving based on pulse width modulation ofa light emitting diode can be represented by

t _(ON)/(t _(ON) +t _(OFF))=t _(ON) /t _(Const)

Then, signals corresponding to the on time t_(R-ON), t_(G-ON), t_(B-ON)of the red light emitting diode 10R, green light emitting diode 101G andblue light emitting diode 101B which compose the area light source unit42 are sent to the LED driving circuit 83. The LED driving circuit 83controls the switching elements 85R, 85G, 85B based on the values of thesignals corresponding to the on time t_(R-ON), t_(G-ON), t_(B-ON) sothat LED driving current is supplied from the light emitting diodedriving circuit 86 to the light emitting diodes 101R, 101G, 101B. As aresult, the light emitting diodes 101R, 101G, 101B emit light for the ontime t_(R-ON), t_(G-ON), t_(B-ON), respectively. Thus, each display areaunit 12 is illuminated with a predetermined luminous intensity.

The state obtained in this manner is indicated by solid lines in FIGS.9A and 9B. In particular, FIG. 9A illustrates a relationship between avalue (x′≡x^(2.2)) obtained by raising the value of an input signalinputted to the liquid crystal display apparatus driving circuit 90 inorder to drive a sub pixel to the 2.2th power and the duty ratio(=t_(ON)/t_(Cout)). FIG. 9B illustrates a relationship between the valueX of a control signal for controlling the light transmittance Lt of asub pixel and the display luminance y. [Step-150]

Meanwhile, the values x_(R), x_(G), x_(B) of the input signals [R, G, B]inputted to the liquid crystal display apparatus driving circuit 90 aresent to the timing controller 91. The timing controller 91 supplies (oroutputs) control signals [R, G, B] corresponding to the input signals[R, G, B] inputted thereto to the sub pixels [R, G, B]. The valuesx_(R), x_(G), x_(B) of the control signals [R, G, B] produced by thetiming controller 91 of the liquid crystal display apparatus drivingcircuit 90 and supplied from the liquid crystal display apparatusdriving circuit 90 to the sub pixels [R, G, B] and the values x_(R),x_(G), x_(B) of the input signals [R, G, B] have relationshipsrepresented by the following expressions (4-1), (4-2) and (4-3),respectively:

X _(R) =f _(R)(b ₁ _(—) _(R) ·x _(R) ^(2.2) +b ₀ _(—) _(R))  (4-1)

X _(G) =f _(G)(b ₁ _(—) _(G) ·x _(G) ^(2.2) +b ₀ _(—) _(G))  (4-2)

X _(B) =f _(B)(b ₁ _(—) _(B) ·x _(B) ^(2.2) +b ₀ _(—) _(B))  (4-3)

where b₁ _(—) _(R), b₀ _(—) _(R), b₁ _(—) _(G), b₀ _(—) _(G), b₁ _(—)_(B) and b₀ _(—) _(B) are constants. Further, since the light sourceluminance Y₂ of the area light source unit 42 is varied for each imagedisplay frame, the control signals [R, G, B] basically have valuesobtained by performing correction (compensation) based on the variationof the light source luminance Y₂ for the values obtained by raising thevalues of the input signals [R, G, B] to the 2.2th power. In particular,in the Embodiment 1 and the Embodiment 2, since the value of the lightsource luminance Y₂ varies for each one image display frame, the valuesx_(R), x_(G), x_(B) of the control signals [R, G, B] are determined andcorrected (compensated for) so that the display luminance secondprescribed value y₂ may be obtained at the light source luminance Y₂(≦Y₁) to control the light transmittance (numerical aperture) Lt of thepixel or sub pixel. Here, the functions f_(R), f_(G), f_(B) of theexpressions (4-1), (4-2) and (4-3) are functions determined in advancefor performing such correction (compensation).

The image display operation for the one image display frame is completedtherewith.

While the present invention has been described based on preferredembodiments thereof, the present invention is not limited to theembodiments. The configuration and structure of the color liquid crystaldisplay apparatus of the transmission type, area light source apparatus,area light source units, liquid crystal display apparatus assemblies anddriving circuits described hereinabove in connection with theembodiments is merely illustrative, and also the members, materials andso forth which are used to compose the configurations and structures areonly illustrative and can be altered suitably. Further, while, in theembodiments described above, the light emitting element assembly 100includes a lens 102 and a cap 130, where the cap 130 and the filler 140function sufficiently as the lens 102 and there is no necessity toprovide a lens 102 separately, the cap 130 and the filler 140 can beregarded as a lens and the lens above the cap 130 can be omitted.

Further, the temperature of each light emitting diode may be supervisedby a temperature sensor such that a result of the supervision is fedback to an area light source unit driving circuit to perform luminancecompensation (correction) or temperature control of an area light sourceunit. Further, while, in the embodiments described above, it is assumedthat the display area of a liquid crystal display apparatus is dividedin P×Q imaginary display area units, under certain circumstances, aliquid crystal display apparatus of the transmission type may have astructure wherein it is actually divided in P×Q display area units.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. An area light source apparatus for illuminating a liquid crystaldisplay apparatus of the transmission type, which has a display areaformed from a plurality of pixels arrayed in a two-dimensional matrix,from the back, comprising: a plurality of light emitting elementassemblies each provided as a light source and each including a lightemitting element and a lens through which light emitted from said lightemitting element passes; and a plurality of dummy lenses disposed in theproximity of each of said light emitting element assemblies andconfigured same as the lenses of said light emitting element assemblies.2. The area light source apparatus according to claim 1, wherein each ofsaid dummy lenses is formed from an inoperative light emitting elementassembly.
 3. The area light source apparatus according to claim 1,wherein each of said dummy lenses is disposed in a region in which lightemitted from the lenses which compose said light emitting elementassemblies is introduced directly into the dummy lens.
 4. The area lightsource apparatus according to claim 1, wherein, in the proximity of anyof said light emitting element assemblies, other ones of said lightemitting element assemblies are disposed.
 5. The area light sourceapparatus according to claim 4, wherein one of said light emittingelement assemblies is disposed in a region in which light emitted fromthe lens of another one of said light emitting element assemblies isintroduced directly into the light emitting element assembly.
 6. Thearea light source apparatus according to claim 5, wherein a lightemitting element assembly group is composed of a plurality of ones ofsaid light emitting element assemblies which are positioned at thevertices of one or a plurality of imaginary regular triangles, and aplurality of ones of said dummy lenses are disposed on the outer side ofthe light emitting element assembly group in such a manner as to bepositioned at the vertices of imaginary regular triangles of the sameshape as that of the imaginary regular triangle.
 7. The area lightsource apparatus according to claim 5, wherein a light emitting elementassembly group is composed of a plurality of ones of said light emittingelement assemblies which are positioned at the vertices of one or aplurality of imaginary squares, and a plurality of ones of said dummylenses are disposed on the outer side of the light emitting elementassembly group in such a manner as to be positioned at the vertices ofimaginary squares of the same shape as that of the imaginary square. 8.The area light source apparatus according to claim 1, wherein, where itis assumed that the display area of the liquid crystal display apparatusis divided into P×Q imaginary display area units, said area light sourceapparatus comprises P×Q area light source units corresponding to the P×Qdisplay area units; the light emitting state of said P×Q area lightsource units being controlled individually; each of said area lightsource units including a light source formed from a plurality of ones ofsaid light emitting element assemblies.
 9. A liquid crystal displayapparatus assembly, comprising: a liquid crystal display apparatus ofthe transmission type having a display area formed from a plurality ofpixels disposed in a two-dimensional matrix; and an area light sourceapparatus for illuminating said liquid crystal display apparatus fromthe back, said area light source apparatus including a plurality oflight emitting element assemblies each provided as a light source andeach including a light emitting element and a lens through which lightemitted from said light emitting element passes; said area light sourceapparatus including a plurality of dummy lenses which are disposed inthe proximity of said light source element assemblies and are same asthe lenses included in said light emitting element assemblies.